The present invention relates to the field of automated manufacturing apparatus and, more particularly, to apparatus for determining the angular orientation of an article, such as a piece part of a product assembly, in preparation for its engagement by a robotic part handling device.
In the interest of improving efficiency and reducing costs, programmable robotic part handling devices are being incorporated into automated product assembly lines. In one type of assembly operation such a robotic device is assigned a task of grasping a part provided at a pick-up station and transferring it to its proper position on the assembly.
In order for the robotic device to successfully locate and grasp the part, its operating program must have, or be supplied with, data specifying the position and angular orientation of the part at the pick-up station. Typically, the robotic device is preprogrammed for a predetermined part position and angular orientation which requires that the part be accurately located at the pick-up station.
One approach to accurate part location is to provide a dedicated part positioning apparatus that is specifically designed to manipulate and feed a particular part into the pick-up station. However, this approach is not very cost effective because in the event of a major change in the structure of the part, or a shift to a new product, the dedicated device generally is rendered obsolete and must be replaced.
A more flexible approach involves the use of a generic type of part positioning apparatus that is easily adapted to handle a variety of different types of parts.
Such apparatus generally comprise a mechanism for receiving a randomly disposed part and manipulating it to achieve the desired position and orientation; an electronic vision system for viewing the part and providing signals indicative of its position and orientation; and a control system responsive to these signals for operating the part manipulation device.
One type of part manipulation device includes a moveable part supporting X-Y stage that is mounted on a turntable for rotation about a vertical axis. In response to inputs from the vision system, the stage is moved along X and Y axes to accurately position the part in a designated area of a horizontal plane centered on the vertical axis about which the turntable rotates. Once the part is so positioned, the vision system operates in an angular orientation mode and provides signals which are utilized to effect rotation of the turntable to achieve the desired angular orientation which is specified by a polar coordinate angle .theta.. For a representative example of this type of generic part positioning apparatus, see U.S. Pat. No. 4,457,664.
While the above noted part positioning apparatus does provide the flexibility of being able to handle a variety of different parts, it does have drawbacks. The moveable X-Y stage tends to be rather expensive and slow in terms of the time required to accurately position a part in the X-Y plane. Also, because the positioning apparatus has to both position and angularly orient the part, it generally requires the employment of a complex and expensive vision system. Typically, the vision system utilizes pattern recognition or template matching schemes which require the generation and processing of large amounts of data to achieve the desired results. Consequently, the part positioning and angular orientation procedure is relatively slow and tends to have an adverse effect on production rate.
Commonly assigned copending application U.S. Ser. No. 747,841 filed by Peter E. Kane on June 24, 1985 and entitled "PART POSITIONING APPARATUS AND METHOD" discloses and claims a generic type of part positioning apparatus which eliminates the need for a moveable X-Y stage and is adapted to operate with a less sophisticated vision system because it is only involved in the angular orientation procedure and does not have to be used for X-Y positioning.
X-Y part positioning is achieved mechanically using a bowl-like part receptacle. The receptacle is mounted for rotation about a central vertical axis and is also configured to be subjected to a vibratory force directed along the vertical axis.
In response to vibrating the receptacle, a part randomly disposed on a concave interior surface of the bowl slides thereover downwardly and toward the center of the bowl, under the influence of gravity. The shape of the interior surface causes the part to assume an equilibrium position in a designated area of a horizontal plane having its center in coincidence with the central vertical axis. Thereafter, the vision system is invoked to sense the angular orientation of the part and feed this information to the control system which effects rotation of the receptacle about the vertical axis until the part supported on the interior surface is in the desired angular orientation for pick up.
Despite reducing the work load of the vision system to the angular orientation phase, commercially available vision systems suitable for this task tend to have relatively slow response times and are rather expensive.
Also, it would be desirable to have a vision system that is operative for viewing a randomly angularly oriented part and quickly providing data specifying its angular deviation from a desired orientation. The acquisition of such information provides for more flexibility in executing the part pick up scheme. That is, rather than being restricted to physically rotating the part to achieve desired orientation, the system designer now has the option of feeding this information directly to the robotic device to adjust the orientation of its part engagement member to that of the part at the pick up station.
Therefore, it is an object of the present invention to provide an apparatus for determining the angular deviation of an article from a desired angular orientation.
Another object is to provide such an apparatus that includes a vision system that is simple in its construction and has a relatively fast response time.
Yet another object is to provide such an apparatus that does not restrict achieving desired angular orientation to physically rotating the article, but rather provides the option of modifying the action of a robotic part handling device to accommodate the angular orientation of a randomly oriented article.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.